This invention relates to process fluid evacuation systems, and more particularly to systems including liquid ring pumps for evacuating process fluids having condensable and incondensable components. As used herein and in the appended claims, "condense" and its variants refer to conversion from a gaseous to a liquid state; "incondensable" refers to vapors or gases which cannot be converted to a liquid state under the conditions normally found in the systems of this invention; and "uncondensed" refers to vapors or gases which are incondensable, and which may also include condensable materials which have not yet condensed.
A liquid ring pump system for evacuating process fluid having condensable and incondensable components is shown in Jennings U.S. Pat. No. 3,315,879. As shown, for example, in FIG. 1 of that patent, suction for operating the evacuation system is supplied by liquid ring pump 1. The process fluid to be evacuated is supplied to condenser 20 via conduit 21. In condenser 20 the process fluid is mixed with condensing liquid supplied from heat exchanger 19 via conduit 26. The condensate and condensing liquid exit from condenser 20 via conduit 29 and are supplied to the suction inlet of liquid ring pump 1. The incondensable remainder of the process fluid exits from condenser 20 via conduit 15 and is supplied to the inlet of jet diffuser 10.
Motivating fluid for jet diffuser 10 is a recirculated portion of the evacuated process fluid supplied at atmospheric pressure from separator 5 via conduit 16. Jet diffuser 10 mixes the process fluid with the motivating fluid to increase the pressure of the process fluid to a suitable suction inlet pressure for liquid ring pump 1. The mixture of process fluid and motivating fluid produced by jet diffuser 10 is supplied to the suction inlet of liquid ring pump 1 via conduit 8.
Liquid ring pump 1 compresses the fluid thus supplied to it and discharges the compressed fluid at approximately atmospheric pressure via conduit 6 to separator 5. Separator 5 separates the liquid and gaseous phases of the fluid supplied to it. A portion of the gaseous phase is recirculated to jet diffuser 10 as mentioned above, while the remainder of the gaseous phase is discharged to the atmosphere. The liquid phase is recirculated through heat exchanger 19 as condensing liquid for condenser 20 and as sealing liquid for liquid ring pump 1. The Jennings patent mentions (column 2, lines 56-58) that the condensing liquid and pump sealing liquid may be alternatively derived from outside sources.
The relatively closed-loop construction of the system described above can be undesirable when the process fluid being evacuated contains corrosive constituents because these constituents may build up or concentrate in the system, thereby reducing the life of the system components. An example of an application in which the process fluid contains corrosive constituents is evacuation of evaporators in phosphoric acid plants.
In view of the foregoing, it is an object of this invention to improve and simplify evacuation systems of the type described above, especially (but not exclusively) those designed for evacuating process fluids containing corrosive constituents.